This invention relates to dental impression materials, in particular dental impression materials curable by ring-opening metathesis polymerization with ruthenium complex catalysts.
Impression materials used in dentistry are one of several types of elastomers, such as polysulfides, condensation silicones, polyethers or polyvinyl siloxanes (addition-curable silicones). These materials are normally two-paste systems that are mixed immediately before use, then placed in contact with the tooth structure. Mixing of the two pastes initiates a chemical reaction that results in the formation of the elastic rubber impression material after setting, thereby forming a negative impression of the tooth structure involved. The addition-curable silicones, which exhibit fast curing speeds and low shrinkages, typically use a platinum-containing hydrosilation catalyst. This type of catalyst necessitates the use of silicon-containing oligomers, which are generally expensive. Also, the platinum-based catalyst can be inactivated by sulfur-containing impurities present in the latex gloves ordinarily used by dentists, as well as by certain medicaments used in the oral cavity. In addition, there may be undesirable hydrogen evolution from the decomposition of the hydrosiloxane cross-linkers that are present in these systems. This may increase the time and effort necessary to take an impression with these materials because extra precautionary steps have to be taken.
In view of these drawbacks, there is a need for dental impression materials that do not exhibit the various sensitivity problems described above.
The present invention provides a composition for use as a dental impression material. The composition comprises a polymerizable resin curable by ring-opening metathesis polymerization (ROMP), a dental filler system, and a ruthenium carbene complex catalyst, whereby the catalyst initiates the ring-opening metathesis polymerization of the composition. The polymerizable resin comprises one or more oligomers or polymers that can be tethered and/or end-capped with functional groups such as cycloalkenyl groups that can undergo a metathesis reaction. To phrase it another way, the polymerizable resin may comprise one or a combination of the following: a polymerizable telechelic oligomer or polymer end-capped with a group curable by ROMP; a polymerizable oligomer or polymer tethered and end-capped with a group curable by ROMP, or a polymerizable tri-functional or quadri-functional oligomer or polymer end-capped with a group curable by ROMP. The main chain is advantageously a polydimethylsiloxane.
In an embodiment of the invention, the composition is a base/catalyst system in which the base paste includes the polymerizable oligomer or polymer and an inorganic dental filler system and in which the catalyst paste includes the metathesis catalyst dissolved in an inert solvent and an inorganic dental filler system. In one exemplary embodiment of the present invention, the base paste further includes a silicone-based sulfosuccinate salt, such as dimethicone copolyol sulfosuccinate, for accelerating the catalyst upon mixing of the base paste and catalyst paste. In another exemplary embodiment of the present invention, the oligomer or polymer is a polydimethylsiloxane tethered and end-functionalized with norbornenyl groups and having between 5 and 5000 dimethylsiloxane units, and the catalyst is a ruthenium carbene complex with at least one of the ligands having a basicity higher than tricyclohexylphosphine. The composition of the present invention exhibits reduced sensitivity to sulfur impurities.